Method of and apparatus for delivering pulp stock at constant tonnage rate



Oct. 18, M o sc R 1,882,991

METHOD OF AND APiARlxTUs FOR DELIVERING PULP STOCK AT CONSTANT TONNAGERATE Y Filed Nov. 14, 19so 4 Sheets-Sheet 1 Oct. 18, 1932. M. o. SCHUR1,882,991 METHOD OF AND APPARATUS FOR DELIVERING PULP STOCK AT CONSTANTTONNAGE RATE Filed Nov. 14, 1930 4 Sheets-Sheet, 2

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- METHOD OF AND APPARATUS FOR DELIVERING PULP; 1

STOCK AT CONSTANT TONNAGE RATE Filed Nov. 14, 1930 4 Sheets-Sheet "3Oct. 18, 1932. M. o. SCHUR 1,882,991

METHOD OF AND APPARATUS FOR DEL]:VERING' PULP STOCK AT CONSTANT TONNAGERATE Filed Nov. 14, 1950 4 Sheets-Sheet 4 Patented Oct. 118, 1932 UNITEDSTATES PATENT OFFICE MILTON O. SCHUR, OE BERLIN, NEW HAMPSHIRE, ASSIGNORTO BROWN COMPANY, OF

- BERLIN, NEW HAMPSHIRE, A CORPORATION OF MAINE mnrnon or AND APPARATUSron DELIVERING PULP sroox AT RATE n CONSTANT TONNAGE Application filedNovember 14, 1930. Serial No. 495,599.

This invention relates to a method of and apparatus for delivering pulpstock at a constant tonnage rate.

i In the maufacture of several articles or substances from wood pulp itis highly important that the pulp be supplied at a constant tonnagerate, that is, that the dry weight of the pulp delivered for a unit oftime should be substantially constant with a very small maximumvariation. This is especially important where the pulp is to be treatedwith measured quantities of chemicals. It is a relatively simple matterto supply a constant volume of pulp stock. By regulating the consistencyof such stock so as automatically to maintain the consistencysubstantially uniform, \a substantially constant tonnage rate ofdelivery can be obtained. In combining the two steps so as to obtain aconstant volume rate of stock having a constant consistency, severalpractical difliculties are encountered. It is an object of thisinvention to provide apparatus which avoids such difficulties and whichis capable of delivering pulp with only slight variations in the tonnagerate.

The present invention includes improvements over the subject matter ofmy Patent No. 1,744,145 granted January 21, 1930. In ordinary millpractice the consistency of pulp stock supplied from storage tanks isliable to vary from time to time owing to a variety of causes such forexample as local dilution caused occansionally by Wash water used incleaning out the beater. Furthermore, one

days run of stock may differ materially in consistency from that ofanother day so that it is necessary to regulate the consistency of stocksupply in order to insure uniformity. To this end the stock which issupplied from the beater must be thicker than that which is delivered ata constant tonnage rate since the consistency is, according to thepresent invention, regulated by diluting the supplied stock andcontrolling the rate of addition of the diluted water. In the apparatusdescribed in my Patent No. 1,744,145, diluting Water is mixed with thesupply stream of stock, the diluted stock being pumped into a vat ortank from which it is metered at a constant rate. The excessdiluted-stock escapes over a suitable dam and fiows back to the supplytank from which it was pumped; This results in a dilution of the stockin the supply tank.

at which it was metered therefrom. The regulating valve, besidesobviating unnecessary variation in the consistency ofthe supply streamof stock also eilects a considerable saving in the power required todrive the p pump for the supply stream. Pumps of the centrifugal typeare frequently used for streams of pulp stock. It is characteristic ofthis type of pump that when working against a closed valve, less poweris required to operate the motor of the pump than when a valve is open,this being due to the fact that when no liquid is being discharger fromthe pump, the liquid within the pump casing merely flows around with thepaddles. When, however, the valve is open, velocity must be imparted tothe incoming stream of liquid to discharge it through the dischargepipe. This requires considerably more power than that required formerely maintaining a circular flow of a. small amount of liquid withinthe ing vat is diverted and caused to flow past the feeler of theregulator at substantially constant speed' This makes possible aconsiderable simplification of the apparatus. A constant velocity offlow of the sampling ing device driven at constant speed. The.

metering device may be a type widely used for feeding pul stock at aconstant volume rate by means a wheel revolving on a horizontal axis topresent to the pool successive com artments formed by a number a of pades. ,To avoid the sticking of pulp in the angles between successiveaddles in a wheel of small size such as is suitable for use in asampling stream, I may block off or fill.

the space between paddles for a short tance from the core of the wheel.The function .of the consistency regulator is to control a supply ofdiluting water which is added to the incoming stream of stock so as tomaintain automatically a substantially constant consistency in the stockentering the metering vat. In order to control the rate of inflow ofdiluted stock into the vat, the supply stream may be controlled by asuitable butterfly valve automatically movable in response to changes inthe direction of variation of the level o fa float on the pool of tstock within the vat. The valve may be located at any convenient point,either in the supply stream of undiluted stock or in the stream ofdiluted stock' as it is about to enter the vat. According to the presentinvention mechanism is provided for handling large streams of pulp. Thisincludes power means for o crating the valve, and automatic contro s forthe power means responsive to changes in the direction of variation oflevel of the pool of stock in the vat. In general, where the opening ofa ate or valve 1n a stream offluid is automatically varied in responseto variations from a mean value of some characteristic of a portion ofthe fluid beyond the valve, such as the pressure or velocity of thefluid at a given point, or as in the present instance the surfacelevelof a pool, the mechanism for automatically controlling the valve usuallycauses the valve to move in a direction to oppose a change in pool levelfrom the mean height. This corrective operation of the valve continuesuntil the level returns to the mean height. if the pool rises, thecontrol mechanism starts to close the valve and continues to close itnot only after the poollevel has started to fall, but until the levelhas fallen back to the mean height. By that time the valve has been shuttoo far, and the level falls rapidly below the mean height, starting thecontrol mechanism to move the valve toward its open position. Thus thereis a tend ency on the part of the automatic controlling dis- Thus,

apparatus to fluctuate violently from one cxtreme to the other so thatthepurpose of the apparatus is largely defeated. According to thepresent invention, this tendency to fluctuate or hunt is reduced to aslow drift between relativelynarrow limits by the use of africtional'connection between a member movable directly in response tochanges in the characteristic to be kept constant and control mechanismfor adjustably moving the valve. In the present instance the directlymovable membemmay be a float on the surface of the pool of pulp stock inthe vat.

Rapid and efiicient mixing apparatus is i mixing tank, the agitatingmeans being capable of forming rapid, turbulent currents in the stock insuch a manner that there is up and downmixing as well as transversemixing. .In this way the diluting water is quickly intermixed with thestock and the diluting effect of the water upon the consistency of thestock stream is quickly felt at the point of discharge from the mixingtank. This makes for lncreased sensitivity in the apparatus as a whole,which is an important and valuable feature. Further; to increase thissensitivity, the feeler element of the consistency regulator ispreferably located close to the outlet of the mixing tank so that thelag between a change of the supply rate of the diluting water and itseffect on the fceler is' reduced to a minimum.

For a more complete understanding of the invention reference may be hadto the description thereof which follows and to the drawings of whicl.,-"Figure 1 illustrates diagrammatically apparatus embodying theinvention.

Figures 2, 3 and 4 are similar views of modified forms of the invention.

Figure 5 shows diagrammatically hydraulic apparatus for controlling thestock level in the metering vat.

Figure 6 vshows on a larger scale a por- 'tion'of the mechanism shown inFigure 5.

Figure 7 shows a modified form of a portion of the invention. 's

Figure" 8 is a perspective view of a modified form of feeler forconsistency regulator.

Referring in detail to Figure 1, 10- represents a supply tank for pulpstock coming l through a supply pipe 11 from a storage tank (not shown)or directly from a beater. Within the tank 10 are a suitable number ofagitators 12 driven by a motor 13 to prevent settling of the fibers andalso-to average up the consistency of the stock received through thepipe 11. The tank 10 is preferably of considerable capacity so thatthere is no abrupt fluctuation in the consistency of the stock takentherefrom. From a point near the bottom of the tank 10 a dischargepipe-14 runs to a centrifugal pump 15; A

second pipe 16 leads from a point about halfway up on the side of thetank 10 to the pump 15. The pipes 14 and 16 may be controlledrespectively by suitable valves 17 and 18. Ordinarily stock is takenfrom the middle level of the tank 10 through the pipe 16, the pipe 14being used when it is desired to empty the tank or in case' the levelshould temporarily falPbelow the orifice of the pipe 16. The pump 15discharges into a pipe 20 which opens into the bottom of a suitablemixing tank 21. \Vithin the pipe '20 is a valve 22 preferably of thebutterfly type which provides a variable supply port for the admissionof liquid into the tank 21. The valve member itself may be in the formof an elliptical plate which fits diagonally across the cylindricalinterior of the pipe when the valve is entirely closed and may be swungto a position in line with the axis of the pipe by a suitable lever 66which may be operated by any convenient apparatus such as .an hydraulicpiston contained in a cylinder 24. Within the mixing tank 21 suitablemixing apparatus may be provided. As shown, this may consists of a pairof marine propellers 25 mounted on a shaft 26 supported a short distanceabove .the bottom of the tank 21. This shaft may bc-connected to asuitable motor 27 for rotation. The blades of the propellers 25 arepreferably of opposite pitch so that they throw streams in oppositedirections against the sides of the tank. This causes a pair of circularcurrents rising at with diluting water at a point just prior to itsentrance into the mixing tank. As soon i as the stock enters the mixingtank, the rapid mixing current-s carry it laterally and upwardly, thepropellers churning the thick stock and the water together to formquickly an evenly diluted stock. If the rate of supply of water throughthe pipe 30 is increased or diminished, this change is almostimmediately felt at the upper end of the mixing tank 21 by reason of therapid circulation of the currents in the tank 21. The diluting wateris'supplied through a suitable pipe 31 which is connected to a standpipe32. From the latter a serigs of overflow pipes 33 lead after describedin detail, so as to maintain a substantially constant consistency in thestock,

passing through the mixing tank 21.

At the upper end of the tank 21 a short "standpipe 35 projects upwardlyinto a metering vat 36 at one end ofwhich is a metering wheel 37. besimilar to that described in my Patent No. 1,744,145, and may have anumber of blades or paddles between which are the compartment-ssuccessively filled by pulp from the. pool in the vat 36 as the meteringwheel rotates. The pulp stock passing through the wheel isdischarged-into a suitable pipe 38 through which it is-conducted toapparatus for further treatment. iVithin the vat 36 is a dam 40 toprovide a spill-way in case of excessive high level of the pulp stock inthe pool. Excess stock spilling over the crest of the .dam 40 may beconducted through a pipe 41 back to the supply tank 10. Ordinarily,however, the surface level of the stock pool in the vat 36 will beautomatically maintained by the valve 22 below the crest of the dam 40so that no diluted stock will be returned to the supply tank 10.

e For the control of the valve -22,'suitable mechanism may be providedincluding a float 42 in the pool of stock in the vat 36. This controlmechanism may take various forms. For example, hydraulically operatedcontrol apparatus is illustrated in Figures 1 and 6. As shown, the float42 maybe connected by a rod 43 to a lever arm 44 which may be pivoted asat 45. This arm carries a pair of spring-pressed friction members 46 and47 adapted to press against opposite side surfaces of the vertical stem50 of a slide valve 51. The pressure of the friction shoes 46 and '47may be provided by a pairof springs 52 and 53, the force of which may beregulated by a pair of adjusting screws 54 and The stem 50 has a neutralor normal position relative to the arm 44. A pair of springs 56 Themetering wheel 37 may and 57 connect the stein 50 with the arm 44 l insuch a way as to tend to maintain thestem in its neutral position and toreturn the stem posed by the friction shoes 46 and 47. The

valve 51 may'slide'in a suitablecasing 60 and may be provided withsuitable ports in a manner well known in the art by which a pressurefluid supply pipe maybe connected 5 with either one of two servicepipes, the other service pipe being simultaneously connected with adischarge pipe. As shown, compressed liquidv or air may besuppliedthrough a supply pipe 61, a discharge pipe 62 being also connected withthe casing 60. A pair of service pipes 63 and 64 extend from the casing60 to the hydraulic cylinder 24 so as to transmit fluid pressure to thechamber above orbelow a piston 65 in the cylinder 24 for the actuationof the valve 22. The piston 65 may be connected with the valve 22 by anysuitable linkage such as a lever arm 66 as shown in Figure 1,.or a geartrain as shown in Figure 5. are provided for the purpose-of steadyingthe operation of the va ve 22 and preventing the apparatus from hunting.This maintains the stock level in the vat 36 at a subdrift betweenpredetermined maximum and minimum limits, which limits may be quiteclose together so there is little variation in the level of the pool.

The operation of the valvecontrol apparatus is as follows: Consideringfirst, by way of comparison, what would happen if the stem 50 werepivoted directly to the arm 44 instead of frictionally connected throughthe shoes 46 and 47, it is evident that a rise or upward drift in thelevel of the pool would cause a rise in the float 42 and the stem 50.This would cause the valve 51 to admit pressure fluid into the servicepipe 64 so as to move the valve 22 toward its closed position and thusto diminish or constrict the supply port for the incoming stream ofstock. When the valve 22 had been closed sutliciently to stop the riseof the pool level, the valve 51 would still be open and would remain 45open until the level of the pool dropped to normal. During the droppingof the pool level to normal, however, the valve 22 would still beclosing so that by the time the valve 51 was closed to stop furtherclosing motion 59 of the valve 22, the level of the pool wouldbe'dropping rapidly owing to the excessive closing of the valve 22. Thiswould carry the pool level below normal, resulting in the operation ofthe valve 51 to move the valve '22 toward its Wide open position. Thisopening motion would continue until the pool sur vface was back tonormal level. Thus the levelof the pool would fluctuate violentlythrough a wide range: Stabilization, how- Q ever, may be accomplished bythe frictional I connection between the valve stem and the lever arm 44.If with-the arm and stem thus connected, the level of the pool shouldrise owing to an oversupply of incoming stock. the

float 42 would rise and would elevate the stem The friction shoes 46 and47 stantially constant level, there being a slow 50 sufliciently to openthe valve. 51 for the admission of pressure to the pipe 64. This wouldcause the piston'65 to move the valve 22 toward its closed position,constricting the supply port. The upward or downward movement of thestem.50 is stopped by engagement of the valve 51 with an end of thecasing when the valve 51 is fully open. During the closing movement ofthe valve 22 the float 42 would continue to rise until the decrease inthe supply stream of stock was sufiicient to stop such rise and to starta recession or downward drift ofthe level. During the rise of the float42 the stem 50 is carried upwardly therewith until its motion is stoppedby engagement of the valve 51 with the upper end of the casing 60.Further rising of the float '42 then results in a slipping of thefriction shoes 46 and 47 on the sides of the stem 50 and an elongationof the spring 57. s As soon as the level of the pool starts its downwarddrift, the stem 50 is at once pulled downwardly by its frictionalengagement by the arm 44 so that the valve 51 is closed and the furtherclosing of the valve 22 is at once stopped. This maintains the supply Yport unchanged until the valve 22 is further actuated. Since the levelof the pool is slightly dropping when the valve 51 is closed, it willordinarily continue to drift downwardly, but at a slow rate. Meanwhilethe tension of the spring 57 will tend to elevate the stem 50 to itsnormal position with respect tothe arm 44, this normal position havingbeen disturbed by additional rise of the arm 44 after the stem hadreached its upper limit. If the rate of descent of the pool level isvery slow so that the upward motion of the stem 50 caused by the spring57 is faster than the downward motion of they stem caused by the descentof the arm 44, the valve 51 may be again actuated to close the valve 22a littlefurther, and hence to caus an additional constriction of thesupply port. If, however, the descent of the pool level is at such arate as to balance the rise of the stem 50 under the action of thespring 57, the pool level will return to its normal height by a gradualfall and at the same time the stem 50 will return to its normal positionrelative to the arm 44 without further change in the supply port. If thefall of the pool level should be at an excessive rate, i. e., more rapidthan the elevation of the stem 50 by the spring 57, then the valve 51 isoperatedto cause opening motion on the part of the valve 22 which wouldenlarge the supply port and tend to check the fall in the level of thepool even before it 11:) reached its normal position. A fall of thelevel of the pool below its normal height would result in similaroperation of theapparatus but in the opposite direction. It is evidentthat with such apparatus, properly 12'.

ing wheel such as the wheel 37. In the oper-- aticn of this wheel thestock in the pool rushes into successive compartments so that there isasurging of stock in the pool which causes the float 42 to bob up anddown constantly. This results in an oscillation of,

the stem up and down and a slight resulting oscillation of the valve 22as the control valve 51 is alternately opened in opposite directions. Arise or fall in the average level of the pool, however, will resultin anelevation or depression of the average height of the stem 50 so that inthe case of a rise, for example, the brief periods of pressure in thepipe 64 would be slightly longer than the periods of pressure in thepipe 63 and there would thus be a resultant movement of the valve 22toward its closed position. This oscillating movement of the float 42and of the parts connected therewith does not interfere with theeffectiveness of the frictional connection between the stem 50 and thearm 44 which keeps the mean level of the pool limited to a slow driftwithin, a narrow range. The constant mo- -tion of the float 42 moreoverassists the action of the shoes 46 and 47 and the springs 56 and 57since any tendency on the part of the shoes to stick against the sidesof the v stem 50 is thus obviated. This mechanism which respondspromptly to'changes of levelof the mean surface of the pool when it isat any level rather than at only normal level,

is particularly important where the .level is liable to be changed notonly by the rate of supply of undiluted pulp from the tank 10 but alsothe rate of supply of diluting water from the pipe 30. It is obviousthat if the consistency of the stock delivered from the Figure 1 arelatively small sampling pipe may be mounted within the supply pipe 35,this sampling pipe 70 leading from the outlet of the mixing tank 21 intoa miniature vat 71 from which the stock may be metered by a meteringwheel 72. The metering wheel 72 for the sampling stream is smallcompared with the metering wheel 37 for the vat. In the small wheel,pulp is'liable to wedge and stick in the angle between the paddles, thuschanging the capacity of the wheel. To obviate such sticking, I may fillor block ofl", as at 69, the spaces between the paddles for a shortdistance from the core of the wheel. The vat 71 is set at such a heightthat the surface of the stock pool therein will have the same level asthe stock spilling over the top of the pipe 35, that is, a substantiallyconstant level. By rotating the metering wheel 72 at a constant rate,the rate of discharge of stock from the vat 71, and hence the rate ofadmission of stock thereinto, will be constant. Thus a constant velocityof flow may be maintained in the pipe 70. In this flow of constantvelocity I may support a suitable feeler 73 in the shape of a ball asshown in Figure 1, or in any other convenient shape such as thehorizontal "rod 730 shown in Figure 8. In order to obtain maximumsensitivity in the apparatus, the orifice of the sampling pipe 70 islocated in the outlet of the mixing tank 21, and the feeler 73 islocated as near as possible to the orifice so as ,to be in a position toreact as soon as possible to a change in the consistency of the stockleaving the mixing tank. The feeler may be located a short distanceabove the orifice of the sampling pipe to avoid uncertainty of itsoperation arising from turbulence of the sampling stream at the orificeof the pipe. The feeler is mounted on a supporting stem 74 which may beattached to a lever arm 75 pivoted at one end as at 76. The stream ofstock rising through the pipe 70 flows against the feeler 73 and pushesit upwardly against a suitable spring 80. The spring may be adjusted tobalance any deslred thrust of the feeler 73 according to the stockconsistency desired, by an adJusting screw 81. If the velocity of thestream in the pipe 70 is maintained constant by operating the meteringwheel 72 at a constant rate, the upward pressure of the stream againstthe feeler 73 will vary as the consistency of the stock. If the stockbecomes thicker; it will push more strongly on the feeler 73 and willswing the lever arm 75 upwardly, whereas a thinning of the stock in thepipe 70 will permit the arm 75 to swing 'below its normal position.Suitable mechanism may be provided to regulate the action of the valve34 for the diluting water in accordance with the motions of the arm 75.For example, the valve 34 may be opened and closed by a reversibleelectric motor 82 controlled by a double throw switch connected with orincluding the free end of the arm 75. As shown, on the arm 75 is acontact member 83 which is adapted to contact with a point 84 when thearm swings up, and with a point 85 when the arm swings down. Thesepoints are connected with a source of electric energy and with the motor82 in such a way as to cause the motor to run in a direction to shut thevalve 34 when the contact member 83 touches the point 85, and to causethe motor to run in a direction to open the valve 34 when the member 83touches the point 84. By locating the points 84 and 85 close togetherthe apparatus can be made to respond at once to very slight variationsin the consistency of the diluted pulp. If, for example, the pulpsupplied from the tank 10 thickens slightly in consistency, theadditional push on the feeler 73 closes the switch 83, 84 causing themotor to open the valve 34 wider to admit diluting water to the mixingtank 21 at an increased rate. The effect of this increase of dilutingwater is quickly felt in the pipe 70 owing to the rapid circulation andchurning of the pulp and water within the mixing tank 21. As a result,the opening motion of the yalve 34 is quickly stopped when theconsistency of the stock in the mixing tank 21 has been restored. to thedesired value. The maintaining of a strictly constant velocity of flowin the pipe 70 is important in that it permits the use of the simpleconsistency regulating shown in Figure 1 in place of more elaborateapparatus which is necessary for successful operation in currents ofvarying velocity. A regulator of the latter type is illustrated in myPatent No. 1,744,145. r

In Figure 2 is illustrated a slightly modified apparatus, the chiefdifference being in the means for supplying undiluted pulp from thesupply tank 10- to the mixing tank 21. Instead of an automatic valve 22as shown in Figure 1, I may extend the supply pipe into a suitable tank79 from which a pipe 86 leads into the bottom of the mixing tank 21. Thediluting water 1s 1ntroduced into the pipe 86 through a pipe 87 whichenters the pipe 86 at a point adjacent to the mixing tank 21. The flowofwater through the pipe 87 may be controlled by a suitable valve 88 whichis actuated by a consistency regulating apparatus responsive to arotating paddle or feeler90, this type of consistency regulatingapparatus being similar to that described in my Patent No. 1,744,145. Asuitable dam 91 is provided in the compartment 79 to provide the spill-Way for excess stock which is pumped into the compartment 79. Thisexcess is led back to the supply tank as through a suitable pipe 92. Asthe feeler 90 of the consistency regulating apparatus 89 is notappreciably affected in its operation by,moderate changes istead in 7;.sampling stream leading into a of flow in the stream in which it Works,it may be supported directly in the stream of stock entering the vat 36.v

As shown, however, it ,may be supported apparatus sampling vat 71 fromwhich the stock is metered at a constant rate by the metering wheel 72,-this metered stock being conveniently discharged into the return ipe 92which leads to the supply tank 10. he quantity of diluted stock returnedto the tank 10 through the sampling meter 71 is not sufiicient to atfectthe average consistency of stock in the tank 10 appreciably. Thiscombination of a rotating feeler and a sampling stream may be used wherean extraordinarily high degree of accuracy in the control of stockconsistency is desired.

In Figure 3M1 electric apparatus for controlling the position ofthevalve 22 is illus' trated, the remainderof the apparatus therein shownbeing substantially identical with that illustrated in Figure 1. Thevalve 22 is located in the stock supply pipe 20 and is operable by asuitable electric motor 95 througha train of gears 96. For controllingthe motor 95 a two-way switch may be employed, this switch including. amovable member 97 adapted to come into Contact with a pair of contactpoints 98 by upward motion or into contact with a pair of con-* tactpoints 99 by downward motion. The switch member 97 ma be carried on a'stem which may be frictionally connected with a lever 44 as hereinbeforedescribed. The motor 95 is of any convenient reversible type, the fieldwindings of the motor being connected respectively with the contactpoints 98 and 99 in such a manner as to operate the motor in onedirection or the other according as the switch member 97 makes contactwith either set of points. To

prevent accidental over=running of the motor which might result indamaging the valve apparatus, .1 may provide suitable limiting switchesand 101. These switches normally close gaps in the circuits through thepoints 98 and 99 respectively. .If the valve 22 is moved to its fullyopened position, a pin 102 engages the switch 101 and opens it, thusbreaking the, circuit tending to operate the motor 95 in the directionto open the valve 22. In like manner, if the motor 95 moves the valve 22to its fully closed position, the pin 103 is provided to engage theswitch 100 and thus to stop the further action of the motor in thisdirection. 1, I

In Figure 4 the electrically operated mechanism for controlling thevalve 22 is combined with an electrically operated consist .1:

ency regulating apparatus. This apparatus may include mechanism similarto that.described in my Patent No. 1,744,145, the control portion of theapparatus being contained in a suitable casing 110. Variations in theresistance offered by the stream of stock to the rotation of the feeler90 cause electric contactsto be made for the operation of a ried toofar. There will customarily follow through which water is supplied tothe stream of stock entering the mixing tank 21. The operation of thisapparatus is substantially the same as that of the apparatus illustratedin Figure 1.

A modified form of apparatus for controlling the valve 22 is shown inFigure 7. The lever arm 44 shown in most of the figures may be dispensedwith, and the vertical rod 43, which is secured to the float 42, mayextend through a pair of suitable guides and 121. A friction collar 122is lightly clamped on the rod 43 between the guides 120 and 121 asbyadjustable springs 123. The collar 122 carries an arm 124 on which aremounted a pair of buntersl25 and 126 adapted to engage and rockrespectively a pair of mercury switches 130and 131 of a well known type.'Each of these switches is normally held open by a.v spring 132. Theswitches are adapted to be connected to an electric motor for operatingthevalve -22 in lieu of the switches illustrated inFigures 3 and 4 forthis purpose. In the operation of the apparatus, if the float causes therod 43 to rise, the hunter rocks the switch to close it. This starts themotor 95 operating in a direction to close the valve 22. Theguide 120may carry an adjustable stop 135 to stop the upward movement ofthecollar 122 and arm 124 at the point where the bunter 125 opens theswitch 130. If the rod 43 continues to rise, it slips through the collar122 ,which is frictionally mounted thereon. Meanwhile the motor 95 isoperating to reduce the incoming stream of stock and thus to lower thestock level in the vat 36. As soon as the level starts to falL-thecollar 122 descends with the rod 43 and the switch 130 is thereuponopened by its spring 132, stopping the motor 95. This prevents theclosing action of the valve 22 from being caraslow downward drift oflevel until the bunter 126 closes the switch 131 and starts the motor95' operating to open the valve 22,

wider. As soon as the level starts to rise, the motor 95 is stopped.This prevents undesirably violent fluctuations of the level of the stockin the metering vat.

I claim:

1. Apparatus of the class described comprising a vat for pulp stockhaving an outlet port and an inlet port, means for controlling theoutflow ofstock through said outlet port, and means for automaticallymaintaining a substantially constant consistency and volume rate ofinflow of stock through said inlet port.'

2. Apparatus of the class described comprising a vat for pulp stockhaving an outlet port andan inlet port, means for controlling theoutflow of stock through said outlet port,

means for automaticallycontrolling the volume flow of stock entering thevat through said inlet port, means for introducing diluting' water intothe stock stream entering the vat prior to its passage through saidinlet' rate, means for maintaining a flow of stock into said vatth'rougasaid inlet port, means for automatically controlling at a point spacedfrom said inlet port the volume flow of said stream in accordance withthe volume of stock in the vat, means for admitting diluting water tosaid stream of stock at a point between the point ofcontrol of saidstream of stock and said inlet port, and means responsive to theconsistency of the stock passing through said inlet port forautomatically controlling the volume flow of said stream of dilutingwater. I

4. Apparatus of the class described comprising a pulp stock vat havingan inlet port and an outlet port, means for causing a substantiallyconstant flow of stoclnfrom said vat through said outlet port,automaticmeans for maintaining an inflow of stock through said inlet portsubstantially equal to said outflow, and means for automaticallymaintain ing a substantially uniform consistency in said inflowingstock, said-last named means lncluding means for lnt-roducing dilutingwater into said inflowing pulp stream prior to its passage through saidinlet port, means' for automatically controlling the supply of saiddiluting water in accordance with the consistency of the pulp passingthrough said inlet port, and means for thoroughly. mixing said dilutingwater into the pulp stock stream prior to its passage through said inletport.

.5..Apparatus of the class described comprising. a vat for pulp stockhaving an inlet for the inflow of stock, a conduit for the stream ofpulp stock inflowing into the tank, a water pipe discharging intosaidconduit to dilute the stock stream, a consistency regulator responsiveto the consistency of the stock entering the vat for controlling theflow of diluting water into said'conduit to maintain the consistency ofthe entering stock substantially constant, a valve in said c'on-' duitat aQpoint upstream relatively to the water pipe connection,'and meansfor regulating said valve automatically in response to the quantity ofstock in said-vat;

6. Apparatus of the. class'described 'comprising a vat for pulp stockhaving an inlet for the inflow of stock into the vat, means for leadingoff a-sampling'str'eam of substantially constantvelocity from theinflowing stream of stock, means for automatically A predetermined rate.

regulating the consistency of the stock in said inflowing stream, saidregulating means including a feeler immersed in said sampling stream,and means for metering stock from I said vat at a predetermined rate.

7. Apparatus of the class described comprising a vat for pulp stockhaving an inlet for the inflow of stock into the vat, means for leadingoil a sampling stream of stock 3 "from the stream entering the vat,means for automatically regulating the consistency of the stock in saidinflowing stream, said-regulating means including a feeler immersed insaid sampling stream, mechanism for main- 5 taining theflow of saidsampling stream at box for rapidly and continuously mixing the contentsthereof, means for supplying a stream of stock to said box, means forsupplying water to said box to dilute the stock supplied thereto, meansresponsive to changes in consistency'of stock leaving the box forautomatically regulating the water supply to,

maintain the stock passing from the box to the vat at-a substantiallyconstant consistency,

and means responsive to changes in the level of stock in the vat forautomatically regulating the rate of delivery of stock to the vat. 9.Apparatus of the class described comprising a vatfor pulp stock, meansfor metering stock from said vat at a constant volume v rate, means forsupplying a stream of stock to said vat including a mixing box adjacentto said vat, means for supplying diluting water to said box, means insaid box for mixing thoroughly the supplied stock and diluting water andfor circulating the mixture rapidly in the box, means for automaticallyregulating the rate of flow of stock entering the box and vat tomaintain the quantity of stock therein substantially constant, andmeansfor regulating the supply of diluting water to maintain the consistencyof the stock flowing into the vat substantially constant, said waterregulating means including means for leading off a sampling stream ofdiluted stock from said box at a constant velocity, and a feelersupported in said sampling stream.

10. Apparatus of theclass described comprising a consistency'regulatorhaving a feeler to be supported in a stream of stock, and

means for maintaining a constant velocity of 1 flow in the portion ofthe stream contiguous to said feeler.

11. Apparatus for regulating the consistency of a delivery stream ofpulp stock, which includes means for leading off from said-deliverystream a sampling stream of stock, a

feeler in said sampling stream, means for positively feeding saidsampling stream at aconstant volume rate of flow, and mechanismresponsive to the resistance of said feeler to I the flow of the stockin said sampling stream for altering the consistency of the stock insaid delivery stream.

12. In combination with apparatus forleading oil a sampling stream ofpulp stock to test and regulate the consistency thereof, means forpositively feeding said sampling stream at a constant volumerate offlow, said means comprising a metering device, and means for drivingsaid device at a constant rate.

13. Apparatus for maintaining substantially constant a characteristic ofa portion ofa stream of fluid depending on the rate an element having alimited range of movement and movable in said range by frictionalengagement with said member.

14. Apparatus for controlling a supply streamof fluid in respdnse tochanges in a characteristic of a portion of the fluid which has passedthe point of supply control, said apparatus including a valve. in saidsupply stream, reversible ower means for moving said valve toward itsopen and closed posi-- tions, a control element movable from anintermediate position to positively limited positions in whichrespectively said power means are operated to move said valve incorresponding directions, a member positively movable in response tochanges in said characteristic, said member having frictional engagementwith said element so as to move-said element to one or the other of itslimiting positions, and spring means between said member and elementtending to maintain said member and element in a predetermined relationto each other.

15. Apparatus for maintaining a pool of liquid at 'a substantiallyconstant level during a continuous inflow and outflow of liquid into andout of said pool, said apparatus comprising a valve in the incomingstream, rover sible power means for moving said valve toward its openand closed positions, and means responsive to changes in level of saidpool for controlling said power means, said power controlling meansincluding a float on said pool, a member positively movable by the riseand fall of said float, and an element frictionally engaged by saidmember and movable thereby between limiting positions in whichrespectively said element causes the. actuation of said power means tomove said-valve correspondingly.

16. Apparatus for maintaining a pool of liquid at a substantiallyconstant level during a continuous inflow and outflow of liquid into andout of said pool, said apparatus comprising a valve movable to regulatethe rate of said inflow of liquid, reversible power means for movingsaid valve toward its open and closed positions, a float on said pool, amember movable positively by rise and fall of said float on said pool,and a control element movable by frictional engagement with said mem herin a narrow range between limiting positions, said control elementhaving a normal intermediate position from which it is movable by a riseof the float to cause said power means to move said valve toward itsclosed position, said element being movable by a fall of said float tothe opposite limiting position to cause said power means to-movesaidvalve toward its open position.

17. Apparatus of theclass described comprising a vat for pulp stockhaving an inlet for the inflow of stock into said vat, a valve forregulating the inflowing stream, a float in said vat, valve-actuatingmeans, and control connections between said float and said actuatingmeans, said connections including an element having a'norrowly limitedrange of motion and a second element positively movable by said floatand in frictional en gagement with said limited element.

18. A metering wheel of small size for a sampling stream of pulp stock,comprising an axis, a plurality of paddles projecting outwardly fromsaid axis, the spaces between successive paddles being blocked off for ashort distance from said axis.

19. A method of maintaining near a predetermined height the surfacelevel of a pool having an inflow and outflow of liquid, and ofminimizing the rate of variation of said level, which comprises varyingthe rate of inflow independently of the quantity of liquid present inthe pool at any moment to oppose variation of surface level, andautomatically controlling the variation of inflow in response to changesin direction of variation of level.

20. A method of maintaining substantially constant the quantity of afluid in abody thereof having a supply stream adding fluid thereto and adischarge stream taking fluid therefrom, which comprises constricting oramplifying one of said streams independently of the quantity of fluidactually in said body at any moment, and controlling said constrictingor amplifying action in response to changes in direction of variation ofsaid quantity.

21. A method of maintaining substantially constant the level of a poolof liquid in a vessel to which liquid is being added through a supplyport and from which liquid is being discharged, which comprisesconstricting the supply port in response to an upward drift of saidlevel from normal until a downward drift sets in, maintaining saidsupply port unchanged during the downward drift to normal level unlessthe rate of said downward drift is excessive or deficient, and enlargingsaid port in response to excessive rate of downward drift oradditionally constricting said port in response to deficient rate ofdownward drift toward normal, said method also comprising enlarging saidsupply port in response to a downward drift of level from normal untilan upward drift sets in, maintaining said supply port unchanged duringsaid upward drift to normal level unless the rate of said upward driftis excessive or deficient, and constricting said port in response toexcessive rate of upward drift or additionally enlarging said port inresponse to deficient rate of upward drift toward normal level;

22. A method of delivering pulp stock at a substantialy constant tonnagerate, which comprises maintaining a pool of stock, metering stock fromsaid pool at a constant volume rate, providing a supply stream of stockfor said pool, diluting the stock in the supply stream to theconsistency desired, and admitt'ing diluted stock to the pool at a ratesubstantialy the same as the rate of discharge of the stock from thepool.

23. A method of delivering pulp stock at a substantially constanttonnage rate, which comprises maintaining a pool of stock, me-

tering stock from said pool at a constant volume rate, providing asupply stream of stock, introducing diluting water into said stream,mixing said water thoroughly with the stock in said stream immediatelyprior to its entrance into said pool, regulating the rate of supply ofdiluting water to maintain the consistency of the mixed dilutedstocksubstantially constant, and controlling the stock supply stream tomaintain a volume rate of admission of diluted stock into said poolsubstantially equal to the rate at which the stock is metered from thepool.

24. A method of delivering pulp stock at a substantially constanttonnage rate, which comprises maintaining a pool of stock, meteringstock from said pool at a constant volume rate, providing a supplystream of stock, introducing diluting water into said stream, mixingsaid water thoroughly with the stock in the stream, regulating the rateof addition of Water to. maintain the consistency of the mixed dilutedstock substantially constant, admitting the diluted stock to the pool,and regulating the flow of the supply stream of undiluted stock so thatits flow added to that of the diluting water substantiallyequals thedischarge flow from the pool.

In testimony. whereof I have aflixed my signature.

MILTON O. SCHUR.

